Composition for the removal of heavy metals from gases

ABSTRACT

A composition, containing vanadium and a support, wherein at least a portion of the vanadium has crystallite sizes of less than about 100 Å as determined by an analytical method such as X-Ray Diffraction, is disclosed. A method of preparing such composition is also disclosed. The composition is employed in a process to remove a heavy metal from a gaseous feed stream which can optionally include a separate mercury adsorption stage.

The invention relates to a composition useful in the removal of heavymetals from a gaseous feed stream. In one aspect the invention relatesto a method of preparing such composition. In yet another aspect theinvention relates to a process for removing heavy metals from a gasstream using the inventive composition and, optionally, a second stageadsorption of the heavy metal.

BACKGROUND OF THE INVENTION

Heavy metals are released during the combustion process of many fossilfuels and/or waste materials. These heavy metals include, for example,arsenic, beryllium, lead, cadmium, chromium, nickel, zinc, mercury andbarium. Most of these heavy metals are toxic to humans and animals. Inparticular, lead is thought to compromise the health and mental acuityof young children and fetuses.

Furthermore, there is every indication that the amount of mercury, andpossibly of other heavy metals, now legally allowed to be released bythose combusting various fossil fuels and/or waste materials, includingcoal burning powerplants, and petroleum refineries, will be reduced byfuture legislation. While a variety of adsorbents are available forcapture of heavy metals (in particular mercury), these adsorbents tendto have low capacities and are easily deactivated by other components inthe gas stream, such as sulfur oxides. We have discovered a materialthat converts an elemental heavy metal to an oxidation state greaterthan zero, even in the presence of sulfur oxides.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an improved vanadiummaterial which when used in the removal of heavy metal results inoxidation of the heavy metal to an oxidation state greater than zero,even in the presence of sulfur oxides and nitrogen oxides.

A further object of this invention is to provide a method for making animproved vanadium material which when used in the removal of heavy metalresults in oxidation of the heavy metal to an oxidation state greaterthan zero, even in the presence of sulfur oxides and nitrogen oxides.

Another object of this invention is to provide an improved process forthe removal of heavy metal from a heavy metal-containing gas whichresults in oxidation of the heavy metal to an oxidation state greaterthan zero, even in the presence of sulfur oxides and nitrogen oxides,with an optional second stage for adsorption of oxidized heavy metal.

In accordance with a first embodiment of the invention, the inventivecomposition comprises vanadium and a support selected from the groupconsisting of: 1) amorphous silica-alumina; 2) a zeolite; 3) a materialcomprising meta-kaolin, alumina, and expanded perlite; 4) alumina; and5) combinations thereof, wherein at least a portion of the vanadium hascrystallite sizes of less than about 100 Å as determined by ananalytical method such as X-Ray Diffraction.

In accordance with a second embodiment of the invention, the inventivecomposition comprises vanadium and a support selected from the groupconsisting of: 1) amorphous silica-alumina; 2) a zeolite; 3) a materialcomprising meta-kaolin, alumina, and expanded perlite; 4) alumina; and5) combinations thereof; heated in the presence of oxygen and a solventto a calcination temperature; wherein the calcination temperature issufficient to volatilize and remove substantially all of the solvent;and wherein said calcination temperature is below the temperature whichwould result in the conversion of greater than about 90 weight percentof the vanadium to vanadium-and-oxygen containing crystalites greaterthan about 100 Å in size.

In accordance with a third embodiment of the invention, the inventivecomposition can be prepared by the method of:

a) incorporating a vanadium compound onto, into, or onto and into asupport selected from the group consisting of: 1) amorphoussilica-alumina; 2) a zeolite; 3) a material comprising meta-kaolin,alumina, and expanded perlite; 4) alumina; and 5) combinations thereof,in the presence of an oxidizing agent and a solvent, to thereby form avanadium incorporated support; and

b) calcining the vanadium incorporated support at a calcinationtemperature; wherein the calcination temperature is sufficient tovolatilize and remove substantially all of the solvent; and wherein thecalcination temperature is below the temperature which would result inthe conversion of greater than about 90 weight percent of the vanadiumto vanadium-and-oxygen-containing crystallites greater than about 100 Åin size, to thereby form the composition.

In accordance with a fourth embodiment of the invention, the inventivecomposition can be used in the removal of heavy metal from a gaseousfeed stream comprising heavy metal by contacting, under heavy metalremoval conditions, the gaseous feed stream with any of the inventivecompositions of embodiments one through three above, with an optionalsecond stage for adsorption of oxidized heavy metal.

Other objects and advantages of the invention will become apparent fromthe detailed description and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

The inventive composition comprises, consists of, or consistsessentially of a support and vanadium.

The support is selected from the group consisting of: 1) amorphoussilica-alumina; 2) a zeolite; 3) a material comprising, consisting of orconsisting essentially of alumina, expanded perlite and meta-kaolin; 4)alumina; and 5) combinations thereof. As used in this disclosure, theterm “Support” refers to a carrier for another catalytic component.However, by no means is a support necessarily an inert material; it ispossible that a support can contribute to catalytic activity andselectivity.

The vanadium is present in said composition, on an elemental vanadiumbasis, in an amount in the range of from about 0.5 to about 50 weight %,preferably from about 1 to about 20 weight %, and most preferably fromabout 1.5 to about 15 weight %, based on the total weight of thecomposition.

In accordance with the first embodiment of the present invention thecomposition comprises, consists of or consists essentially of vanadiumand a support, as above described, wherein at least a portion,preferably at least about 10 weight percent, more preferably at leastabout 80 weight percent, and most preferably at least about 95 weightpercent, of the vanadium of the composition has a crystalite size lessthan about 100 Å, more preferably less than about 30 Å, and mostpreferably less than about 20 Å as determined by an analytical methodsuch as X-Ray diffraction.

In accordance with the second embodiment of the present invention, thecomposition is preferably heated in the presence of oxygen and a solventto a calcination temperature. The calcination temperature is preferablysufficient to volatilize and remove substantially all of the solvent,more preferably greater than about 125° C., and most preferably greaterthan about 150° C. The calcination temperature is also preferably belowthe temperature which would result in the conversion of greater thanabout 90 weight percent of the vanadium tovanadium-and-oxygen-containing crystallites greater than about 100 Å insize; more preferably below about 400° C.; even more preferably belowabout 375° C.; and most preferably below about 350° C. The solvent ispreferably an aqueous solution of oxalic acid.

The composition is preferably heated, as described above, for a timeperiod in the range of from about 0.1 hours to about 24 hours, and morepreferably in the range of from about 1 hour to about 4 hours.

In accordance with the third embodiment of the present invention, theinventive composition can be prepared by the method of, and a method isprovided including:

a) incorporating a vanadium compound onto, into, or onto and into asupport selected from the group consisting of: 1) amorphoussilica-alumina; 2) a zeolite; 3) a material comprising meta-kaolin,alumina, and expanded perlite; 4) alumina; and 5) combinations thereof,in the presence of an oxidizing agent and a solvent, to thereby form avanadium incorporated support; and

b) calcining the vanadium incorporated support at a calcinationtemperature; wherein the calcination temperature is sufficient tovolatilize and remove substantially all of the solvent, more preferablygreater than about 125° C., and most preferably greater than about 150°C.; and wherein the calcination temperature is below the temperaturewhich would result in the conversion of greater than about 90 weightpercent of the vanadium to vanadium-and-oxygen-containing crystallitesgreater than about 100 Å in size, more preferably below about 400° C.;even more preferably below about 375° C.; and most preferably belowabout 350° C.

The vanadium compound can be any vanadium containing compound capable ofincorporation onto and/or into a support. Preferably, the vanadiumcompound is selected from the group consisting of 1) ammoniummetavanadate, 2) an alkali metavanadate of the formula MVO₃, wherein Mcan be an alkali metal selected from Group IA, and combinations thereof;and 3) combinations of any two or more thereof. The most preferablevanadium compound is ammonium metavanadate.

The oxidizing agent can be any agent capable of oxidizing vanadium, andpreferably is hydrogen peroxide or oxygen. The solvent is preferably anaqueous solution of oxalic acid. Also, the calcination time period is asdescribed in the second embodiment.

Also, preferably the support comprises alumina, meta-kaolin, andexpanded perlite, and is prepared by the method of:

1) adding expanded perlite to a mixture of alumina and water to therebyform a second mixture;

2) adding meta-kaolin to the second mixture to thereby form a thirdmixture;

3) adding a dispersant to the third mixture to thereby form a fourthmixture; and

4) calcining the fourth mixture to thereby form the support.

The calcining of step 4) preferably comprises heating the fourth mixtureto a temperature in the range of from about 100° C. to about 200° C. fora first time period in the range of from about 0.5 hour to about 2hours; and subsequently heating the fourth mixture to a temperature inthe range of from about 500° C. to about 750° C. for a second timeperiod in the range of from about 0.5 hour to about 2 hours.

In accordance with the fourth embodiment of the present invention, theinventive composition can be used in the removal of heavy metal from agaseous feed stream comprising heavy metal by a process comprising,consisting of, or consisting essentially of contacting, in a contactingzone, under heavy metal removal conditions, the gaseous feed stream withany of the inventive compositions, and combinations thereof, ofembodiments one through three above. A gaseous product stream iswithdrawn from the contacting zone. The gaseous feed stream is typicallya combustion gas; and is more typically a stack gas derived from thecombustion of coal. The gaseous feed stream can also further comprisecompounds selected from the group consisting of sulfur oxides, CO₂,water, nitrogen oxides, HCl, and combinations of any two or morethereof.

The contacting of the gaseous feed stream with the inventive compositionis preferably carried out at a temperature in the range of from about100 to about 325° C, more preferably from about 125 to about 275° C.,and most preferably from about 150 to about 225° C.

The heavy metal typically comprises a metal selected from the groupconsisting of arsenic, beryllium, lead, cadmium, chromium, nickel, zinc,mercury, barium, and combinations of any two or more thereof. The heavymetal most typically comprises mercury.

When the heavy metal is mercury, the mercury is typically present in thegaseous feed stream in an amount in the range of from about 0.1 to about10,000 μg/m³, more typically in the range of from about 1 to about 800μg/m³ and most typically from about 3 to about 700 μg/m³.

The composition preferably converts at least a portion of the heavymetal in the gaseous feed stream to an elevated oxidation state. In thecase of mercury, the composition preferably converts at least a portionof the mercury contained in the gaseous feed stream from a zerooxidation state to a +1 or a +2 oxidation state and also preferablyremoves mercury. “At least a portion”, as used in this paragraph, canmean at least 20 weight %, preferably at least 30 weight %, and morepreferably at least 50 weight % mercury based on the total amount ofmercury contained in the gaseous feed stream.

The gaseous product stream preferably contains less than about 80 weight%, more preferably less than about 90 weight %, and most preferably lessthan about 95 weight % of the mercury contained in the gaseous feedstream.

The gaseous product stream is optionally contacted with a separateadsorbent in an adsorption zone. The adsorbent can be any adsorbentcapable of adsorbing a heavy metal. More preferably, the adsorbentcomprises, consists of or consists essentially of a material selectedfrom the group consisting of a zeolite, amorphous carbon, andcombinations thereof. The amorphous carbon can be an activated carbon oran activated charcoal. A treated gaseous product stream is withdrawnfrom the adsorption zone and contains less than 80 weight %, preferablyless than 90 weight %, and more preferably less than 95 weight % of theheavy metal contained in the gaseous feed stream.

EXAMPLES

The following examples are intended to be illustrative of the presentinvention and to teach one of ordinary skill in the art to make and usethe invention. These examples are not intended to limit the invention inany way.

Types of Supports

-   A. Fresh commercially available FCC catalyst.-   B. Equilibrium FCC catalyst removed from a commercial unit.-   C. Support prepared from alumina, perlite, and metakaolin clay. The    procedure involves mixing 254 grams of Vista Dispal alumina, 900    grams of de-ionized water, and 300 grams of expanded crushed    perlite. To this slurry, ASP-600 metakaolin clay from Engelhard and    240 grams of Darvan 821 A are added. The material is then heated to    150° C., held there for one hour, and then heated to 650° C. for one    hour. This material is ground to 20 to 40 mesh particles (420 to 840    microns) before the impregnation step.-   D. Gamma Alumina.-   E. Delta Alumina.    Preparation of Sorbents

The preparation of the sorbents involves the addition of vanadium to thevarious supports. To a 2 molar solution of ammonium metavanadate(NH₄VO₃) in oxalic acid, hydrogen peroxide (30 wt. %) is added drop wiseuntil approximately 10% of the weight of the ammonium metavanadate isobtained. (The red color of the solution suggests that vanadium is in +5oxidation state). The solution is then impregnated onto the support byincipient wetness. Between impregnation steps, the vanadium-impregnatedsupport is heated to 110° C. in a drying oven. After the finalimpregnation step, the material is calcined at a temperature that canrange from 150° to 450° C.

Evaluation of Sorbents to Remove Mercury

The following procedure is used to test the ability of the sorbent toremove mercury from a gas stream. Mercury is added by passing an airstream at room temperature through a gas bottle containing elementalmercury. For the moist air runs, the air is passed through a bubblerprior to passing through the gas bottle containing mercury. The mercurycontaining gas stream is then passed through a sample tube containingapproximately 0.5 to 1.5 grams of the sorbent to be tested. The tube islocated in a furnace where the temperature can range from 110° to 170°C. The inlet and outlet elemental mercury concentrations are measuredusing a Jerome Mercury Analyzer. The efficiency of mercury removal isdetermined from the amount of mercury entering and leaving the solidsorbent, and is defined as the difference between the inlet and outletmercury concentrations divided by the inlet concentration.

The table below summarizes the results obtained when passing mercury indry or moist air (as indicated in the Table) over the various sorbents.In all cases, the contacting zone temperature is 150° C. while the gashourly space velocity ranges from 2500 to 6000 hour −1. The removalefficiency is determined as a function of mercury uptake; i.e., thecumulative amount of mercury already adsorbed on the sample in units ofmicrograms of mercury per gram of sorbent (μg/g).

TABLE 1 Removal efficiency of mercury as function of support, amount ofvanadium, calcination temperature, and mercury uptake. CalcinationRemoval Temperature Mercury Efficiency Support Air Wt. % V (° C.) Uptake(μg/g) (%) A Dry 11.2 300 2000 100 4000 98 9500 100 B Dry 2.8 300 400 982000 96 3500 90 B Dry 5.6 300 500 99 2500 99 5500 99 Dry 11.2 150 400 98800 60 B Dry 11.2 300 400 100 800 90 1200 86 B Dry 11.2 350 400 99 B Dry11.2 375 300 70 B Dry 11.2 450 400 50 C Dry 8.9 300 5000 100 20000 10035000 100 D Dry 8.9 300 103 100 246 100 326 100 D Dry 8.9 350 13 100 103100 558 100 D Dry 8.9 450 18 67 67 24 90 9 D Moist 8.9 300 211 99 1659100 4436 100 E Dry 2.6 200 69 99 397 99 969 96 E Dry 2.6 450 88 97 31057 437 40 E Dry 2.6 600 131 94 2052 91 4642 91 E Moist 2.6 200 387 901104 96 1734 59 E Moist 2.6 600 335 76 827 47 1169 8

The results in Table 1 clearly indicate that the efficiency of mercuryremoval depends upon various characteristics of the sorbent. Althoughall supports give high removal efficiencies, the perlite containingsupport (C) is more effective than the gamma alumina support (D) whichis slightly more effective than the fresh FCC catalyst (A) that in turnis slightly more effective than the used FCC catalyst (B) which is moreeffective than the delta alumina support (E). The results also indicatethat the performance of the sorbent strongly depends upon calcinationtemperature with calcination temperatures above 350° C. leading to lesseffective sorbents. The results further indicate that the presence ofmoisture in the air/mercury feed has a substantial effect on sorbentefficiency.

Characterization of Sorbents

In an effort to understand the relationship between structure andperformance, a variety of techniques were used to characterize thesorbents. These include nuclear magnetic resonance, X-ray diffraction,and Raman spectroscopy. Description of these techniques and the resultsobtained are given below.

Solid-state ⁵¹V NMR using magic angle spinning (MAS) and static widelinemethods were used to characterize some of the sorbents. Spectra wereobtained on a Varian INOVA 400 NMR spectrometer, operating at 399.8 MHzfor ¹H, and 105.1 MHz for ⁵¹V, using a MAS probe with 5 mm whitezirconia rotors spinning at 10 to 12 KHz, or non-spinning (static). ⁵¹Vchemical shift was determined by using NH₄VO₃ as a secondary chemicalshift reference at −576 ppm (and using VOCl₃ as a primary chemical shiftreference at 0 ppm). This was accomplished by running the sample at twodifferent spinning frequencies, 10 and 12 kHz, to distinguish theisotropic chemical shift peak from the sidebands. The V-51 MAS andstatic spectra of 11.2 wt. % vanadium supported on used FCC catalyst(support B) show a distinct difference between the two low temperaturecalcined samples (300° and 350° C.) and the two higher temperaturecalcined samples (375° and 450° C). The low temperature samples havebroader peaks in the MAS but narrower width of static spectra. Theseresults suggest that vanadium oxide is predominantly in an amorphousstate for calcination temperatures of 350° C. and below. However, as thecalcination temperature increases, the vanadium forms crystalline V₂O₅.

X-ray diffraction measurements were made on a PanAnalytical Expert ProDiffractometer with an accelerator linear array detector and a copper Kαsource. Three samples were evaluated by XRD−11.2 wt. % vanadiumsupported on a used FCC catalyst (support B) that was calcined either at300°, 350°, or 450° C. The 450° C. calcined samples show evidence ofcrystalline V₂O₅. The lower temperature calcined samples show noevidence of crystalline V₂O₅, but do indicate a presence of amorphousvanadates.

A LabRam Infinity Raman Microscope (JY Horiba, Inc.) was used toevaluate 11.2 wt. % vanadium samples on used FCC catalysts (support B)calcined at various temperatures. The instrument utilizes an OlympusBX40 microscope and is enclosed in a light-sensitive box to avoidfluorescence interferences from room lights. A 532 nm laser and an 80times objective are used for all analyses. The results indicate thatcalcination temperatures above 350° C. induce the formation ofcrystalline V₂O₅. The Raman results suggest the presence ofpolymeric-type amorphous vanadium at calcination temperatures of 350° C.and lower.

1. A composition comprising vanadium and a support selected from the group consisting of: 1) amorphous silica-alumina; 2) a zeolite; 3) a material comprising meta-kaolin, alumina, and expanded perlite; 4) alumina; and 5) combinations thereof, wherein at least a portion of said vanadium has crystallite sizes of less than about 100 Å as determined by an analytical method such as X-Ray Diffraction.
 2. A composition in accordance with claim 1 wherein said vanadium is present in said composition, on an elemental vanadium basis, in an amount in the range of from about 0.5 to about 50 wt. percent, based on the total weight of said composition.
 3. A composition in accordance with claim 1 wherein said vanadium is present in said composition, on an elemental vanadium basis, in an amount in the range of from about 1 to about 20 wt. percent, based on the total weight of said composition.
 4. A composition in accordance with claim 1 wherein said vanadium is present in said composition, on an elemental vanadium basis, in an amount in the range of from about 1.5 to about 15 wt. percent, based on the total weight of said composition.
 5. A composition consisting essentially of vanadium and a support selected from the group consisting of: 1) amorphous silica-alumina; 2) a zeolite; 3) a material comprising meta-kaolin, alumina, and expanded perlite; 4) alumina; and 5) combinations thereof, wherein at least a portion of said vanadium has crystallite sizes of less than about 100 Å as determined by an analytical method such as X-Ray Diffraction.
 6. A composition consisting of vanadium and a support selected from the group consisting of: 1) amorphous silica-alumina; 2) a zeolite; 3) a material comprising meta-kaolin, alumina, and expanded perlite; 4) alumina; and 5) combinations thereof, wherein at least a portion of said vanadium has crystallite sizes of less than about 100 Å as determined by an analytical method such as X-Ray Diffraction.
 7. A composition comprising vanadium and a support selected from the group consisting of: 1) amorphous silica-alumina; 2) a zeolite; 3) a material comprising meta-kaolin, alumina, and expanded perlite; 4) alumina; and 5) combinations thereof, heated in the presence of oxygen and a solvent to a calcination temperature; wherein said calcination temperature is sufficient to volatilize and remove substantially all of the solvent; and wherein said calcination temperature is below the temperature which would result in the conversion of greater than about 90 weight percent of the vanadium to vanadium-and-oxygen-containing crystallites greater than about 100 Å in size.
 8. A composition in accordance with claim 7 wherein said solvent is an aqueous solution of oxalic acid.
 9. A composition in accordance with claim 7 wherein said composition is heated for a time period in the range of from about 0.1 to about 24 hours.
 10. A composition in accordance with claim 7 wherein said composition is heated for a time period in the range of from about 1 to about 4 hours.
 11. A composition in accordance with claim 7 wherein said vanadium is present in said composition, on elemental vanadium basis, in an amount in the range of from about 0.5 to about 50 wt. percent, based on the total weight of said composition.
 12. A composition in accordance with claim 7 wherein said vanadium is present in said composition, on elemental vanadium basis, in an amount in the range of from about 1.0 to about 20 wt. percent, based on the total weight of said composition.
 13. A composition in accordance with claim 7 wherein said vanadium is present in said composition, on elemental vanadium basis, in an amount in the range of from about 1.5 to about 15 wt. percent, based on the total weight of said composition.
 14. A composition in accordance with claim 7 wherein said calcination temperature is below about 400° C.
 15. A composition in accordance with claim 7 wherein said calcination temperature is above about 125° C. and wherein said calcination temperature is below about 375° C.
 16. A composition in accordance with claim 7 wherein said calcination temperature is above about 150° C. and wherein said calcination temperature is below about 350° C.
 17. A process comprising: a) contacting, in a contacting zone, a gaseous feed stream comprising a heavy metal and oxygen with the composition of claim 1; and b) withdrawing a gaseous product stream from said contacting zone.
 18. A process as recited in claim 17 wherein said gaseous product stream contains less heavy metal than said gaseous feed stream.
 19. A process as recited in claim 17 wherein said gaseous feed stream further comprises a compound selected from the group consisting of sulfur oxides, CO₂, water, nitrogen oxides, HCl, and combinations of any two or more thereof.
 20. A process as recited in claim 17 wherein said gaseous feed stream is a combustion gas.
 21. A process as recited in claim 17 wherein said gaseous feed stream is a stack gas derived from the combustion of coal.
 22. A process as recited in claim 17 wherein said contacting of step a) is carried out at a temperature in the range of from about 100 to about 325° C.
 23. A process as recited in claim 17 wherein said contacting of step a) is carried out at a temperature in the range of from about 125 to about 275° C.
 24. A process as recited in claim 17 wherein said contacting of step a) is carried out at a temperature in the range of from about 150 to about 225° C.
 25. A process as recited in claim 17 wherein said heavy metal comprises a metal selected from the group consisting of arsenic, beryllium, lead, cadmium, chromium, nickel, zinc, mercury, barium, and combinations of any two or more thereof.
 26. A process as recited in claim 25 wherein said heavy metal is mercury.
 27. A process as recited in claim 26 wherein said composition converts at least a portion of said mercury in said gaseous feed stream from a zero oxidation state to a+1 or a+2 oxidation state.
 28. A process as recited in claim 26 wherein said mercury is present in said gaseous feed stream in an amount in the range of from about 0.1 to about 10,000 μg/m³.
 29. A process as recited in claim 26 wherein said mercury is present in said gaseous product stream in an amount in the range of from about 1 to about 800 μg/m³.
 30. A process as recited in claim 26 wherein said mercury is present in said gaseous product stream in an amount in the range of from about 3 to about 700 μg/m³.
 31. A process as recited in claim 26 wherein said gaseous product stream contains less than about 80 weight % of the mercury contained in said gaseous feed stream.
 32. A process as recited in claim 26 wherein said gaseous product stream contains less than about 90 weight % of the mercury contained in said gaseous feed stream.
 33. A process as recited in claim 26 wherein said gaseous product stream contains less than about 95 weight % of the mercury contained in said gaseous feed stream.
 34. A process as recited in claim 17 wherein said gaseous product stream is contacted, in an adsorption zone, with an adsorbent selected from the group consisting of a zeolite, amorphous carbon, and combinations thereof.
 35. A process as recited in claim 34 wherein said composition oxidizes at least a portion of said heavy metal in said gaseous feed stream to an elevated oxidation state.
 36. A process as recited in claim 34 wherein said heavy metal is mercury and wherein said composition oxidizes at least a portion of said mercury in said gaseous feed stream from a zero oxidation state to a+1 or a+2 oxidation state.
 37. A process as recited in claim 34 wherein a treated gaseous product stream is withdrawn from said adsorption zone, and wherein said treated gaseous product stream contains less than about 80 weight % of the heavy metal contained in the gaseous feed stream.
 38. A process as recited in claim 34 wherein a treated gaseous product stream is withdrawn from said adsorption zone, and wherein said treated gaseous product stream contains less than about 90 weight % of the heavy metal contained in the gaseous feed stream.
 39. A process as recited in claim 34 wherein a treated gaseous product stream is withdrawn from said adsorption zone, and wherein said treated gaseous product stream contains less than about 95 weight % of the heavy metal contained in the gaseous feed stream.
 40. A process comprising: a) contacting, in a contacting zone, a gaseous feed stream comprising a heavy metal and oxygen with the composition of claim 14; and b) withdrawing a gaseous product stream from said contacting zone.
 41. A process as recited in claim 40 wherein said gaseous product stream contains less heavy metal than said gaseous feed stream.
 42. A process as recited in claim 40 wherein said gaseous feed stream further comprises a compound selected from the group consisting of sulfur oxides, CO₂, water, nitrogen oxides, HCl, and combinations of any two or more thereof.
 43. A process as recited in claim 40 wherein said gaseous feed stream is a combustion gas.
 44. A process as recited in claim 40 wherein said gaseous feed stream is a stack gas derived from the combustion of coal.
 45. A process as recited in claim 40 wherein said contacting of step a) is carried out at a temperature in the range of from about 100 to about 325° C.
 46. A process as recited in claim 40 wherein said contacting of step a) is carried out at a temperature in the range of from about 125 to about 275° C.
 47. A process as recited in claim 40 wherein said contacting of step a) is carried out at a temperature in the range of from about 150 to about 225° C.
 48. A process as recited in claim 40 wherein said heavy metal comprises a metal selected from the group consisting of arsenic, beryllium, lead, cadmium, chromium, nickel, zinc, mercury, barium, and combinations of any two or more thereof.
 49. A process as recited in claim 48 wherein said heavy metal is mercury.
 50. A process as recited in claim 49 wherein said composition converts at least a portion of said mercury in said gaseous feed stream from a zero oxidation state to a+1 or a+2 oxidation state.
 51. A process as recited in claim 49 wherein said mercury is present in said gaseous feed stream in an amount in the range of from about 0.1 to about 10,000 μg/m³.
 52. A process as recited in claim 49 wherein said mercury is present in said gaseous product stream in an amount in the range of from about 1 to about 800 μg/m³.
 53. A process as recited in claim 49 wherein said mercury is present in said gaseous product stream in an amount in the range of from about 3 to about 700 μg/m³.
 54. A process as recited in claim 49 wherein said gaseous product stream contains less than about 80 weight % of the mercury contained in said gaseous feed stream.
 55. A process as recited in claim 49 wherein said gaseous product stream contains less than about 90 weight % of the mercury contained in said gaseous feed stream.
 56. A process as recited in claim 49 wherein said gaseous product stream contains less than about 95 weight % of the mercury contained in said gaseous feed stream.
 57. A process as recited in claim 40 wherein said gaseous product stream is contacted, in an adsorption zone, with an adsorbent selected from the group consisting of a zeolite, amorphous carbon, and combinations thereof.
 58. A process as recited in claim 57 wherein said composition oxidizes at least a portion of said heavy metal in said gaseous feed stream to an elevated oxidation state.
 59. A process as recited in claim 57 wherein said heavy metal is mercury and wherein said composition oxidizes at least a portion of said mercury in said gaseous feed stream from a zero oxidation state to a+1 or a+2 oxidation state.
 60. A process as recited in claim 57 wherein a treated gaseous product stream is withdrawn from said adsorption zone, and wherein said treated gaseous product stream contains less than about 80 weight % of the heavy metal contained in the gaseous feed stream.
 61. A process as recited in claim 57 wherein a treated gaseous product stream is withdrawn from said adsorption zone, and wherein said treated gaseous product stream contains less than about 90 weight % of the heavy metal contained in the gaseous feed stream.
 62. A process as recited in claim 57 wherein a treated gaseous product stream is withdrawn from said adsorption zone, and wherein said treated gaseous product stream contains less than about 95 weight % of the heavy metal contained in the gaseous feed stream. 